This invention relates to sphere interchanges and in particular to a sphere interchange for a unidirectional meter proving device.
In various pipeline systems, particularly those used for conveying liquid petroleum products, the accuracy of the pipeline flowmeter is of such critical importance that meter proving or testing devices are utilized at frequent intervals to check the calibration of the meter. The meter prover conventionally includes a calibrated section of pipe which may be connected in series with the flowmeter. A pipeline sweeping device or sphere, which is sized to make snug contact with the wall of the calibrated section, is introduced into the pipeline and sweeps the known volume of the calibrated section during a proving run. If the dimensions of the conduit between the flowmeter and the calibrated section remain constant and if no liquid leakage occurs, the volume of liquid passing through the flowmeter during the time the sphere traverses the calibrated section will be equal to the volume of the calibrated section. Conventionally, the calibrated section is defined by a pair of switches which respectively start and stop a register associated with the flowmeter. The registered flow is then compared with the known volume of the calibrated section as a check on, or calibration of, the meter.
In a unidirectional meter prover, the calibrated section is conventionally formed as a "U" or loop, and the sphere is always launched into the same end of the loop. A sphere interchange between the ends of the loop catches the sphere at the downstream leg of the loop after a proving run, and on command begins the next proving run by transferring the sphere to the upstream leg. During a proving run, the interchange must be sealed to prevent any leakage of liquid across the interchange from the upstream (high pressure) side of the loop to the downstream (low pressure) side.
Because the accuracy of the prover depends upon there being no fluid leakage around the interchange seal or around the sphere, a successful prover interchange should have a long-lived and easily monitored seal, and should provide for easy removal of the sphere for periodic inspection or replacement. The interchange should protect the sphere from wear or damage from the moving parts of the interchange, both in normal operation and in the event of a malfunction. Throughout its operating cycle it should also minimize hydraulic effects caused by shunting of liquid across the interchange and should provide positive control of the sphere. The interchange is also desirably compact and adaptable for use in various orientations relative to the prover loop so as to fit into the limited space available in many applications. Finally, it is desirable that the interchange be simple and rugged and that it not be vulnerable to sludge or debris in the pipeline.
Various unidirectional meter provers are presently known. For the most part they include a calibrated loop having its outlet end physically above its inlet end, and a sphere interchange consisting of a launch tee by which the sphere is introduced by gravity into the prover loop, a receiving tee for separating the sphere from the outlet end of the loop and a sphere transfer device for receiving a sphere from the receiving tee and beginning a proving run by launching it into the launch tee.
None of the prior art systems possesses all of the previously mentioned desirable attributes.
One type of unidirectional meter prover system makes use of more than one sphere. In these systems, while one sphere traverses the calibrated section, the other sphere or spheres remain in the interchange and act as a seal. A second approach, using a single sphere, has a spherical valve in the interchange which seals the interchange and transfers the sphere from the outlet end to the inlet end of the calibrated loop. The limitations of both these types are well known and need no further discussion here.
A third type of system, also using a single sphere, utilizes a reciprocating piston as one of the mating parts of the interchange seal. The piston also controls the transfer of the sphere through the interchange. The present invention is an improved interchange for a meter proving system of this third type. Examples of recently proposed systems of this type are Park et al., U.S. Pat. No. 3,246,666 (1966); Layhe, U.S. Pat. No. 3,504,523 (1970); Grove et al., U.S. Pat. No. 3,638,475 (1972); Simmons, U.S. Pat. No. 3,738,153 (1973); Gloster Saro Ltd., British Patent Specification 1,201,762, (published 1970); and General Descaling Company Ltd., British Patent Specification 1,203,735 (published 1970).
The Gloster Saro, Grove et al. and Simmons patents disclose dual resilient seals which may be monitored by observing the pressure between the seals. These seals, however, require careful alignment, are vulnerable to debris and are subject to wear caused by shearing forces. Sphere removal is accomplished in these prior art systems by the costly expedient of providing separate seals at the ends of the transfer device (Park et al., Layhe, Gloster Saro), or by making the wall through which the piston rod extends removable and adding external guides for keeping the wall and piston aligned (Grove et al., General Descaling), or by inserting an external ramp into the transfer device (Simmons). All of these recent devices, except Grove et al., require a stop of some sort to hold the sphere in the receiver tee at the end of a proving run until the next proving run is begun, and the Grove et al prover interchange permits flow through it between proving runs. All except Park et al lack positive means for supporting and aligning the piston member throughout its travel, and the Park et al approach requires a dificult alignment of bearings and of seals.